submarine canyon

Shaded relief image of seven submarine canyons imaged on the continental slope off New York, using multibeam echosounder data. The Hudson Canyon is the furthest to the left. Perspective view shaded relief image of the San Gabriel and Newport submarine canyons off Los Angeles The Congo Canyon off southwestern Africa, about 300 km (190 mi) visible in this view Heavily canyoned northern margin to the Biscay abyssal plain, with the Whittard Canyon highlighted Bering Sea showing the larger of the submarine canyons that cut the margin Sketch showing the main elements of a submarine canyon A submarine canyon is a steep-sided valley cut into the seabed of the continental slope, sometimes extending well onto the continental shelf, having nearly vertical walls, and occasionally having canyon wall heights of up to 5 km (3 mi), from canyon floor to canyon rim, as with the Great Bahama Canyon. Just as above-sea-level canyons serve as channels for the flow of water across land, submarine canyons serve as channels for the flow of turbidity currents across the seafloor. Turbidity currents are flows of dense, sediment laden waters that are supplied by rivers, or generated on the seabed by storms, submarine landslides, earthquakes, and other soil disturbances. Turbidity currents travel down slope at great speed (as much as 70 km/h (43 mph)), eroding the continental slope and finally depositing sediment onto the abyssal plain, where the particles settle out.

About 3% of submarine canyons include shelf valleys that have cut transversely across continental shelves, and which begin with their upstream ends in alignment with and sometimes within the mouths of large rivers, such as the Congo River and the Hudson Canyon. About 28.5% of submarine canyons cut back into the edge of the continental shelf, whereas the majority (about 68.5%) of submarine canyons have not managed at all to cut significantly across their continental shelves, having their upstream beginnings or "heads" on the continental slope, below the edge of continental shelves.